Currently there is no REST API endpoint to directly convert some JSON record into a Frame object. Thus, the only way forward for you would be to first write the data to a CSV file, then upload it to h2o using POST /3/PostFile, and then parse using POST /3/Parse.

(Note that POST /3/PostFile endpoint is not in the documentation. This is because it is handled separately from the other endpoints. Basically, it's an endpoint that takes an arbitrary file in the body of the post request, and saves it as "raw data file").

The same job is much easier to do in Python or in R: for example in order to upload some dataset into h2o for scoring, you only need to say